Map data based on J.-P. Boudot & V. J. Kalkman (eds.),Atlas of the European Dragonflies and Damselflies

General

➤ a tiny American species, which in Europe occurs only on the Azores (females only)

Classification

• suborder: Zygoptera (damselflies); family: Coenagrionidae

Conservation status

• IUCN Red List Europe: Vulnerable

Scientific name

• Ischnura hastata (Say, 1839)

Distribution

• click or tap the Map button above

Notes

• The all-female population on the Azores is unique among the world's odonata in that it reproduces parthenogenetically. The hypothesis that this might be the case was first postulated in 1990 when attempts to collect males from the islands proved unsuccessful (as they have remained since). In recent years the Azores population has been the subject of intensive study (notably by Adolfo Cordero and Olalla Lorenzo), and proof of the females' ability to reproduce parthenogenetically was provided by Cordero in his laboratory in Vigo, Spain, when he managed to raise several consecutive generations (of females only, of course) from Azorean larvae.

• When and why the islands' population has become parthenogenetic is not clear. First discovered (though initially misidentified) in 1938, it is now believed that the population has been present on the islands for at least a few centuries (but not millennia), and was initially transported to the islands from America on strong westerly winds. It is unknown whether the initial population consisted of males and females but something then started to push the population towards parthenogenesis or whether only parthenogenetic females colonized the islands.

• As a phenomenon, parthenogenesis is not all that uncommon among insects and other animals, and in some cases can be explained in terms of bacterial infections (e.g. by the Wolbachia bacterium). But in the case of Ischnura hastata no evidence of bacterial infection has been found among the Azorean females. Whether today's parthenogenesis in this population is the result of some other, as yet unknown environmental factor which over time eliminated the males from the population, or whether the females themselves decided they might as well do without the males, will probably remain a matter of speculation for some time yet. What is clear, though, is that even if only a small part of the females in a population start to develop a tendency towards asexual, parthenogenetic reproduction, then ultimately that parthenogenesis could become widespread among the population, with fewer and fewer females being available to males and, consequently, fewer and fewer male offspring being produced.

• there are no androchrome females

Habitat

• any pond with a rich vegetation

Dimensions

• typical body length: 20-27 mm; hindwing: 11-15 mm

Male

Thorax

• the lower side of the thorax and the antehumeral stripe are pale green

Abdomen

• the top of the abdomen is black on S1-S2, yellow with black markings on S3-S7, and completely yellow on S8-S10

➤ the pterostigma in the forewing is bright orange-red and is considerably larger than the grey-black pterostigma in the hindwing

• the pterostigma in the forewing is not directly connected to the costa (i.e. the wing's leading edge), but is separated from and connected to it by a light-coloured petiole; where the pterostigma 'ought to be' the costa itself is whitish yellow (rather than black). No other known species has this kind of in-wing pterostigma.

Female

Thorax

• in immature females the side of the thorax is bright orange (a colour form known as aurantiaca); with age this orange colour is gradually replaced by green or grey

• old females develop a light pruinescence on the thorax

Abdomen

• in immature females the top of the abdomen is bright orange except on S6 and S7 (and S8), where it is black (with age the amount of black increases); the side of the abdomen is bright orange

• in mature females the top of the abdomen is entirely black; in side view the lower part is whitish

• the abdomen has a vulvar spine underneath S8

• old females develop a light pruinescence on the abdomen

Wings

• the pterostigma is uniformly brown in both wings

Photographs

• all of our photos below were made in Florida in 2013

Click on a thumbnail to display the photograph (at 1200 x 800 pixels) in a new window.